This invention generally relates to radar systems and techniques for determining target location and more specifically to a radar processing system and method for detecting and maintaining targets in the presence of multiple mainlobe and multiple sidelobe interference sources.
One of the problems facing surveillance and fire control radar systems today is target detection and estimation of target angle in the presence of severe jamming interference. Typically, jamming is in the form of a high power transmission designed to impair a radar system""s performance. Jamming may comprise a signal modulated with noise or other disruptive information. The object of typical jammers is to impair the performance of a radar system""s receiving electronics and/or obscure the display. The source of jamming interference may be mobile or may be relatively stationary (e.g., land based systems).
The problem of target detection and estimation of target angle in the presence of jamming interference is particularly important for next generation radar systems used in missile defense. Recently, there has been increases emphasis toward a goal of implementing radar systems in airborne and spaceborne platforms for large area surveillance in addition to surface radars which can be ground based or shipboard based. A problem associated with achieving this goal is developing a radar system capable of detecting targets while rejecting unwanted information such as jammers and clutter.
Radar systems implementing antenna arrays typically form beam patterns comprising a central beam, i.e., main lobe, and surrounding minor lobes, i.e., sidelobes. Typically, it is desired to have a narrow mainlobe having high gain, and low sidelobes. To detect a desired target and reject unwanted clutter and jamming, the mainlobe is steered toward the target of interest. The desired target within the mainlobe is enhanced and the response to clutter and jamming outside the mainlobe is attenuated. However, if a jammer is located within the mainlobe, it becomes difficult to detect the target of interest. This problem is exacerbated in the situation where multiple jammers exist.
Radar systems have been developed to cancel a single jammer in the mainlobe. Such a system is described in U.S. Pat. No. 5,600,326 issued to Yu et al., which is incorporated herein by reference in its entirety. However, these systems require a priori knowledge of the jammer location. Thus, a need exists for a radar system having the ability to detect a target of interest in the presence of multiple mainlobe jammers. A need also exists for a radar system having the capability to cancel multiple mainlobe jammers without requiring a priori knowledge of jammer locations. Further, a need exists for a radar system having the capability to detect a target of interest in the presence of multiple mainlobe and multiple sidelobe jammers.
A system and method for detecting a radar target of interest in the presence of radar jamming interference include a sub-array beamformer, a sum and difference beamformer, a weight calculator, a composite beamformer, and a monopulse ratio calculator. A plurality of sub-arrays is formed from antenna array element data. Respective sum and difference beams are formed for each of the plurality of sub-arrays. Sum and difference weights are formulated in accordance with the sum and difference beams, respectively. Composite sum beams are formed in accordance with the sum weights and the sum beams, and composite difference beams are formed in accordance with the difference weights and the difference beams. Composite beams are formed such that at least one null of each of the composite beams is steered toward an interference and a boresight gain of each of the plurality of sub-arrays is maintained.